This invention relates to a process for the separation of gaseous streams under elevated pressures by means of fractional condensation.
The separation of gaseous streams by fractional condensation is utilized on an industrial scale for obtaining different boiling point fractions. Such a process is described, for example, in "Linde-Berichte aus Technik und Wissenschaft" [Linde Reports on Science and Technology] 45:9 (1979). In this conventional process, hydrocarbon fractions and recycle hydrogen are obtained from a Fischer-Tropsch synthesis cycle; for this purpose, the crude gas is cooled in stages to provide separate recoverable hydrocarbon condensates. By arranging the condensation stages at suitable temperature levels, it is possible to obtain fractions of a desired composition.
In complex large-scale chemical plants, it is often necessary to purify or fractionate a plurality of gaseous streams containing essentially the same components, but not necessarily in the same concentrations. Furthermore, such individual gaseous streams are also generally obtained at different pressure levels, and process conditions dictate that the purified or fractionated streams are recycled, at least in substantial portions, at these same pressure levels. To comply with these criteria, alternatives have been employed for the processing of the various gaseous streams: On the one hand, the gaseous streams can be combined and processed together at a suitable pressure level and the purified gaseous stream can then be restored to the suitable pressure, optionally after having been divided, and then conducted to its respective destination; or, alternatively, mutually independent and distinct separation facilities can be utilized for each process stream. Combined processing is disadvantageous especially when working up gaseous streams having widely different pressures, since significant compression energy must be expanded for adapting the individual process streams to a common pressure level for the purifying steps, either by compression of crude gas introduced under low pressure or by recompression of expanded high-pressure gas. Conversely, the use of independent and distinct separation facilities for each process stream is costly insofar as the advantage of scale is lost. Furthermore, in both procedures, the recovery of valuable light components, e.g., hydrogen, should be conducted in an economical manner, and in this connection there is ample room for increased yields.